1. Field of the Invention
The invention relates in general to a color processing apparatus, and more particularly to a color processing apparatus for reducing cross color.
2. Description of the Related Art
Ordinary screens, such as CRT TV monitors or liquid crystal TV monitors for instance, adopt composite video or S video as the format of the source video. Composite video, labeled as Vcomp, is a quadrature modulated signal and includes two formats, namely NTSC and PAL:Vcomp—PAL=Y+U sin ωt°±V cos ωt+timingVcomp—NTSC=Y+Q sin (ωt+33°)±I cos (ωt+33°)+timingwherein, Y is the luminance, U and V (or I and Q) are chrominance C. For the convenience of explanation, the chrominance C here below includes U and V.
FIG. 1 is a block diagram of an ordinary display apparatus. The composite video Vcomp, having been received by display apparatus 100, is separated into the image data of luminance Y and that of chrominance C by a decoder 110 according to the above formula, and then displayed by a display module 120.
FIG. 2 is a diagram showing the amplitude-frequency relationship for luminance Y and chrominance C. NTSC composite video adopts a bandwidth of about 6 MHz, the carrier wave of the chrominance C has a higher frequency of 3.58 MHz, while the carrier wave of luminance Y has a lower frequency. Therefore, the ordinary decoder 100 can separate Y from C.
However, the luminance Y of the pixel on a diagonal edge still contains a component of high frequency, and can be mixed with high-frequency chrominance C. Consequently, the signal of chrominance C may be mixed with the signal of luminance Y, causing cross color and generating rainbow colors.